Benzoic (acid)
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Benzoic acid is a white (or colorless) solid organic compound with the formula , whose
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
consists of a benzene ring () with a carboxyl ()
substituent A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...
. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, which was for a long time its only source. Benzoic acid occurs naturally in many plants and serves as an intermediate in the biosynthesis of many secondary metabolites. Salts of benzoic acid are used as
food preservative Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
s. Benzoic acid is an important precursor for the industrial synthesis of many other organic substances. The salts and esters of benzoic acid are known as benzoates .


History

Benzoic acid was discovered in the sixteenth century. The dry distillation of gum benzoin was first described by Nostradamus (1556), and then by Alexius Pedemontanus (1560) and Blaise de Vigenère (1596).
Justus von Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at t ...
and
Friedrich Wöhler Friedrich Wöhler () FRS(For) HonFRSE (31 July 180023 September 1882) was a German chemist known for his work in inorganic chemistry, being the first to isolate the chemical elements beryllium and yttrium in pure metallic form. He was the firs ...
determined the composition of benzoic acid. These latter also investigated how
hippuric acid Hippuric acid ( Gr. ''hippos'', horse, ''ouron'', urine) is a carboxylic acid and organic compound. It is found in urine and is formed from the combination of benzoic acid and glycine. Levels of hippuric acid rise with the consumption of phenoli ...
is related to benzoic acid. In 1875 Salkowski discovered the
antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as crypto ...
properties of benzoic acid, which was used for a long time in the preservation of benzoate-containing cloudberry fruits.


Production


Industrial preparations

Benzoic acid is produced commercially by partial oxidation of toluene with oxygen. The process is catalyzed by cobalt or manganese
naphthenate Naphthenic acids (NAs) are a mixture of several cyclopentyl and cyclohexyl carboxylic acids with molecular weight of 120 to well over 700 atomic mass units. The main fraction are carboxylic acids with a carbon backbone of 9 to 20 carbons. McKee et ...
s. The process uses abundant materials, and proceeds in high yield. : The first industrial process involved the reaction of benzotrichloride (trichloromethyl benzene) with
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has m ...
in water, using iron or iron salts as catalyst. The resulting
calcium benzoate Calcium benzoate refers to the calcium salt of benzoic acid. When used in the food industry as a preservative, its E number is E213 (INS number 213); it is approved for use as a food additive in the EU, USA and Australia and New Zealand. The f ...
is converted to benzoic acid with hydrochloric acid. The product contains significant amounts of chlorinated benzoic acid derivatives. For this reason, benzoic acid for human consumption was obtained by dry distillation of gum benzoin. Food-grade benzoic acid is now produced synthetically.


Laboratory synthesis

Benzoic acid is cheap and readily available, so the laboratory synthesis of benzoic acid is mainly practiced for its pedagogical value. It is a common undergraduate preparation. Benzoic acid can be purified by recrystallization from water because of its high solubility in hot water and poor solubility in cold water. The avoidance of organic solvents for the recrystallization makes this experiment particularly safe. This process usually gives a yield of around 65%.


By hydrolysis

Like other
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix ''cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...
s and amides, benzonitrile and benzamide can be hydrolyzed to benzoic acid or its conjugate base in acid or basic conditions.


From Grignard reagent

Bromobenzene can be converted to benzoic acid by "carboxylation" of the intermediate
phenylmagnesium bromide Phenylmagnesium bromide, with the simplified formula , is a magnesium-containing organometallic compound. It is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide is a Grignard reagent. It is o ...
. This synthesis offers a convenient exercise for students to carry out a Grignard reaction, an important class of carbon–carbon bond forming reaction in organic chemistry.


Oxidation of benzyl compounds

Benzyl alcohol and
benzyl chloride Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colorless liquid is a reactive organochlorine compound that is a widely used chemical building block. Preparation Benzyl chloride is prepared indust ...
and virtually all benzyl derivatives are readily oxidized to benzoic acid.


Uses

Benzoic acid is mainly consumed in the production of phenol by
oxidative decarboxylation Oxidative decarboxylation is a decarboxylation reaction caused by oxidation. Most are accompanied by α- Ketoglutarate α- Decarboxylation caused by dehydrogenation of hydroxyl carboxylic acids such as carbonyl carboxylic acid, malic acid, isocitr ...
at 300−400 °C:. :C6H5CO2H + 1/2 O2 -> C6H5OH + CO2 The temperature required can be lowered to 200 °C by the addition of catalytic amounts of copper (II) salts. The phenol can be converted to cyclohexanol, which is a starting material for nylon synthesis.


Precursor to plasticizers

Benzoate plasticizers, such as the glycol-, diethyleneglycol-, and triethyleneglycol esters, are obtained by transesterification of methyl benzoate with the corresponding
diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. The most common industrial diol is e ...
. These plasticizers, which are used similarly to those derived from
terephthalic acid Terephthalic acid is an organic compound with formula C6H4(CO2H)2. This white solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several million tonnes are produced annua ...
ester, represent alternatives to phthalates.


Precursor to sodium benzoate and related preservatives

Benzoic acid and its salts are used as
food preservative Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
s, represented by the E numbers
E210 Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, wh ...
,
E211 Sodium benzoate is the sodium salt of benzoic acid, widely used as a food preservative (with an E number of E211) and a pickling agent. It appears as a white crystalline chemical with the formula C6H5COONa. Production Sodium benzoate is comm ...
, E212, and E213. Benzoic acid inhibits the growth of mold, yeast and some bacteria. It is either added directly or created from reactions with its sodium, potassium, or calcium salt. The mechanism starts with the absorption of benzoic acid into the cell. If the intracellular pH changes to 5 or lower, the anaerobic fermentation of glucose through phosphofructokinase is decreased by 95%. The efficacy of benzoic acid and benzoate is thus dependent on the pH of the food. Benzoic acid, benzoates and their derivatives are used as preservatives for acidic foods and beverages such as citrus fruit juices ( citric acid), sparkling drinks ( carbon dioxide),
soft drinks A soft drink (see § Terminology for other names) is a drink that usually contains water (often carbonated), a sweetener, and a natural and/or artificial flavoring. The sweetener may be a sugar, high-fructose corn syrup, fruit juice, a s ...
( phosphoric acid), pickles ( vinegar) and other acidified foods. Typical concentrations of benzoic acid as a preservative in food are between 0.05 and 0.1%. Foods in which benzoic acid may be used and maximum levels for its application are controlled by local food laws. Concern has been expressed that benzoic acid and its salts may react with
ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
(vitamin C) in some soft drinks, forming small quantities of carcinogenic benzene.


Medicinal

Benzoic acid is a constituent of
Whitfield's ointment Whitfield's ointment is an acidic ointment used for the topical treatment of dermatophytosis, such as athlete's foot. It can have a slight burning effect that goes away after a few minutes. It is named after Arthur Whitfield (1868–1947), a Briti ...
which is used for the treatment of fungal skin diseases such as ringworm and athlete's foot. As the principal component of gum benzoin, benzoic acid is also a major ingredient in both tincture of benzoin and Friar's balsam. Such products have a long history of use as topical antiseptics and inhalant decongestants. Benzoic acid was used as an expectorant,
analgesic An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It ...
, and antiseptic in the early 20th century.


Niche and laboratory uses

In teaching laboratories, benzoic acid is a common standard for calibrating a
bomb calorimeter A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanica ...
.


Biology and health effects

Benzoic acid occurs naturally as do its esters in many plant and animal species. Appreciable amounts are found in most berries (around 0.05%). Ripe fruits of several '' Vaccinium'' species (e.g., cranberry, ''V. vitis macrocarpon''; bilberry, ''V. myrtillus'') contain as much as 0.03–0.13% free benzoic acid. Benzoic acid is also formed in apples after infection with the fungus ''
Nectria galligena ''Neonectria ditissima'' (syn. ''Neonectria galligena'') is a fungal plant pathogen. It causes cankers that can kill branches of trees by choking them off. Apple and beech trees are two susceptible species. Host range ''Neonectria ditissima ...
''. Among animals, benzoic acid has been identified primarily in omnivorous or phytophageous species, e.g., in viscera and muscles of the
rock ptarmigan The rock ptarmigan (''Lagopus muta'') is a medium-sized game bird in the grouse family. It is known simply as the ptarmigan in the UK. It is the official bird for the Canadian territory of Nunavut, where it is known as the ''aqiggiq'' (ᐊᕿ ...
(''Lagopus muta'') as well as in gland secretions of male muskoxen (''Ovibos moschatus'') or Asian bull elephants (''
Elephas maximus ''Elephas'' is one of two surviving genera in the family of elephants, Elephantidae, with one surviving species, the Asian elephant, ''Elephas maximus''. Several extinct species have been identified as belonging to the genus, extending back to ...
''). Gum benzoin contains up to 20% of benzoic acid and 40% benzoic acid esters. In terms of its biosynthesis, benzoate is produced in plants from cinnamic acid. A pathway has been identified from phenol via
4-hydroxybenzoate 4-Hydroxybenzoic acid, also known as ''p''-hydroxybenzoic acid (PHBA), is a monohydroxybenzoic acid, a phenolic derivative of benzoic acid. It is a white crystalline solid that is slightly soluble in water and chloroform but more soluble in polar ...
.


Reactions

Reactions of benzoic acid can occur at either the aromatic ring or at the carboxyl group.


Aromatic ring

: Electrophilic aromatic substitution reaction will take place mainly in 3-position due to the electron-withdrawing
carboxylic group In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
; i.e. benzoic acid is ''meta'' directing.


Carboxyl group

Reactions typical for
carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s apply also to benzoic acid. * Benzoate esters are the product of the acid catalysed reaction with
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
s. * Benzoic acid amides are usually prepared from
benzoyl chloride Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula . It is a colourless, fuming liquid with an irritating odour, and consists of a benzene ring () with an acyl chloride () substituent. It i ...
. * Dehydration to
benzoic anhydride Benzoic anhydride is the organic compound with the formula (C6H5CO)2O. It is acid anhydride of benzoic acid and the simplest symmetrical aromatic acid anhydride. It is a white solid. Preparation and reactions It is usually prepared by the dehydra ...
is induced with
acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a col ...
or phosphorus pentoxide. * Highly reactive acid derivatives such as
acid halides In organic chemistry, an acyl halide (also known as an acid halide) is a chemical compound derived from an oxoacid by replacing a hydroxyl group () with a halide group (, where X is a halogen). If the acid is a carboxylic acid (), the compound c ...
are easily obtained by mixing with
halogenation In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, ...
agents like
phosphorus chlorides In chemistry, there are three series of binary phosphorus halides, containing phosphorus in the oxidation states +5, +3 and +2. All compounds have been described, in varying degrees of detail, although serious doubts have been cast on the existen ...
or thionyl chloride. * Orthoesters can be obtained by the reaction of alcohols under acidic water free conditions with benzonitrile. * Reduction to
benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. ...
and benzyl alcohol is possible using DIBAL-H, LiAlH4 or sodium borohydride. *
Decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...
to benzene may be effected by heating in quinoline in the presence of copper salts.
Hunsdiecker decarboxylation The Hunsdiecker reaction (also called the Borodin reaction or the Hunsdiecker–Borodin reaction) is a name reaction in organic chemistry whereby silver salts of carboxylic acids react with a halogen to produce an organic halide. It is an exa ...
can be achieved by heating the silver salt. :


Safety and mammalian metabolism

It is excreted as
hippuric acid Hippuric acid ( Gr. ''hippos'', horse, ''ouron'', urine) is a carboxylic acid and organic compound. It is found in urine and is formed from the combination of benzoic acid and glycine. Levels of hippuric acid rise with the consumption of phenoli ...
. Benzoic acid is metabolized by
butyrate-CoA ligase Butyryl-coenzyme A (or butyryl-CoA) is the coenzyme A-containing derivative of butyric acid. It is acted upon by butyryl-CoA dehydrogenase and an intermediary compound of ABE fermentation. Butyryl-CoA is a precursor to and converted from crotonyl- ...
into an intermediate product, benzoyl-CoA, Substrate/Product which is then metabolized by glycine ''N''-acyltransferase into hippuric acid. Substrate/Product Humans metabolize toluene which is also excreted as hippuric acid. For humans, the World Health Organization's International Programme on Chemical Safety (IPCS) suggests a provisional tolerable intake would be 5 mg/kg body weight per day. Cats have a significantly lower tolerance against benzoic acid and its salts than
rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...
s and
mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
. Lethal dose for cats can be as low as 300 mg/kg body weight. The oral for rats is 3040 mg/kg, for mice it is 1940–2263 mg/kg. In Taipei, Taiwan, a city health survey in 2010 found that 30% of dried and pickled food products had benzoic acid.


References


External links

* *
ChemicalLand
{{DEFAULTSORT:Benzoic Acid Excipients Phenyl compounds E-number additives